全文获取类型
收费全文 | 284篇 |
免费 | 13篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 34篇 |
地球物理 | 46篇 |
地质学 | 81篇 |
海洋学 | 23篇 |
天文学 | 73篇 |
自然地理 | 38篇 |
出版年
2022年 | 1篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 8篇 |
2014年 | 7篇 |
2013年 | 22篇 |
2012年 | 26篇 |
2011年 | 19篇 |
2010年 | 13篇 |
2009年 | 27篇 |
2008年 | 15篇 |
2007年 | 13篇 |
2006年 | 12篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有298条查询结果,搜索用时 15 毫秒
151.
Patrick F. Roche Christopher Packham David K. Aitken Rachel E. Mason 《Monthly notices of the Royal Astronomical Society》2007,375(1):99-104
Spectroscopy at 8–13 μm with T-ReCS on Gemini-S is presented for three galaxies with substantial silicate absorption features, NGC 3094, NGC 7172 and NGC 5506. In the galaxies with the deepest absorption bands, the silicate profile towards the nuclei is well represented by the emissivity function derived from the circumstellar emission from the red supergiant, μ Cephei which is also representative of the mid-infrared absorption in the diffuse interstellar medium in the Galaxy. There is spectral structure near 11.2 μm in NGC 3094 which may be due to a component of crystalline silicates. In NGC 5506, the depth of the silicate absorption increases from north to south across the nucleus, suggestive of a dusty structure on scales of tens of parsecs. We discuss the profile of the silicate absorption band towards galaxy nuclei and the relationship between the 9.7-μm silicate and 3.4-μm hydrocarbon absorption bands. 相似文献
152.
153.
154.
Rachel Tiller 《Ocean & Coastal Management》2011,54(5):374-380
The Svalbard Fisheries Protection Zone is an international institution on the brink of being challenged in a critical phase of being institutionalized as a Norwegian property regime. The potential disturbance comes from the zooplankton redfeed, a new and valuable resource harvestable within the zone. Though the pressures on Norway’s inspection routines in the zone are challenged at times, this article suggests that the zone as a management regime is a surprisingly robust institution still. Nevertheless, in such a critical phase it is important not to allow possible exogenous shocks to appear, and creating a separate redfeed regime for the plankton will allow the Norwegian government to bypass this possible disturbance and allow for continued solidification of the zone into an EEZ for Norway. 相似文献
155.
Noam Slonim Rachel Somerville Naftali Tishby Ofer Lahav 《Monthly notices of the Royal Astronomical Society》2001,323(2):270-284
A new method for classification of galaxy spectra is presented, based on a recently introduced information theoretical principle, the information bottleneck . For any desired number of classes, galaxies are classified such that the information content about the spectra is maximally preserved. The result is classes of galaxies with similar spectra, where the similarity is determined via a measure of information. We apply our method to ∼6000 galaxy spectra from the ongoing 2dF redshift survey, and a mock-2dF catalogue produced by a cold dark matter (CDM) based semi-analytic model of galaxy formation. We find a good match between the mean spectra of the classes found in the data and in the models. For the mock catalogue, we find that the classes produced by our algorithm form an intuitively sensible sequence in terms of physical properties such as colour, star formation activity, morphology, and internal velocity dispersion. We also show the correlation of the classes with the projections resulting from a principal component analysis. 相似文献
156.
Moody Rachel Schmidt Brian Alcock Charles Goldader Jeffrey Axelrod Tim Cook Kem H. Marshall Stuart 《Earth, Moon, and Planets》2003,92(1-4):125-130
We present preliminary results of the analysis of the first 500 squaredegrees of the Southern Edgeworth-Kuiper belt Survey, a large sky survey whichran from January 2000 to January 2003 and comprises 2900° in total. Early testspredict that we should discover ~10 bright TNOs in our data, doubling the currentknown population. 相似文献
157.
Matt Rovero Diana Cutt Rachel Griffiths Urszula Filipowicz Katherine Mishkin Brad White Sandra Goodrow Richard T. Wilkin 《Ground Water Monitoring & Remediation》2021,41(4):62-75
Published literature for reported sorption coefficients (Kd) of eight anionic per- and polyfluoroalkyl substances (PFAS) in soil was reviewed. Kd values spanned three to five log units indicating that no single value would be appropriate for use in estimating PFAS impacts to groundwater using existing soil-water partition equations. Regression analysis was used to determine if the soil or solution parameters might be used to predict Kd values. None of the 15 experimental parameters collected could individually explain variability in reported Kd values. Significant associations between Kd and soil calcium and sodium content were found for many of the selected PFAS, suggesting that soil cation content may be critical to PFAS sorption, as previously noted in sources like Higgins and Luthy (2006), while organic carbon content was significant only at elevated levels (>5%). Unexplained discrepancies between the results from studies where PFAS were introduced to soil and desorbed in the laboratory and those that used material from PFAS-impacted sites suggest that laboratory experiments may be overlooking some aspects critical to PFAS sorption. Future studies would benefit from the development and use of standardized analytical methods to improve data quality and the establishment of soil parameters appropriate for collection to produce more complete data sets for predictive analysis. 相似文献
158.
Karanam Kishore Kumar Debadatta Swain Sherine Rachel John Geetha Ramkumar 《Climate Dynamics》2011,37(9-10):1961-1973
Owing to the importance of middle atmosphere, recently, a Middle Atmospheric Dynamics (MIDAS) program was carried out during the period 2002?C2007 at Thumba (8.5°N, 77°E). The measurements under this program, involving regular radiosonde/rocket flights as well as atmospheric radars, provided long period observations of winds and temperature in the middle atmospheric region from which waves and oscillations as well as their forcing mechanisms particularly in the low-latitude middle atmosphere could be analyzed. However, a detailed analysis of the forcing mechanisms remains incomplete due to the lack of important measurements like ozone which is a significant contributor to atmospheric dynamics. Presently, profiles of ozone are available from TIMED/SABER (Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broad Emission Radiometry) satellite globally from about 15 to 100?km, over multiple years since 2002. In this regard, a comprehensive study has been carried out on ozone and its variability at Quasi Biennial Oscillation (QBO) and Semiannual Oscillation (SAO) scales using TIMED/SABER ozone observations during the MIDAS campaign period. Before using the TIMED/SABER ozone measurements, an inter-comparison has been carried out with in situ measurements of ozone obtained under the Southern Hemisphere Additional Ozonesondes (SHADOZ) campaign for the year 2007 at few stations. The inter-comparison showed very good agreement between SABER and ozonesonde derived ozone profiles. After validating the SABER observations, ozone profiles are used extensively to study the QBO and SAO along with temperature and winds in the 20?C100?km height region. It is known that the SAO in mesosphere and stratosphere are in opposite phases, but the present study for the first time reports the aspect of opposite phases in the mesosphere itself. Thus, the present work attempts to study the long-period oscillations in stratosphere and mesosphere in ozone, temperature and winds simultaneously for the first time over this latitude. These observations provided a unique opportunity to explore long-period oscillations in chemistry, dynamics and thermal structure of the middle atmosphere simultaneously. 相似文献
159.
Jennifer M.K. O'KeefeErika R. Neace Edward W. LemleyJames C. Hower Kevin R. HenkeGregory Copley Rachel S. HatchAnne B. Satterwhite Donald R. Blake 《International Journal of Coal Geology》2011,87(2):150-156
Vent emissions of the Old Smokey coal fire, Floyd County, Kentucky, were studied in May and July, 2010. Vent emissions were generally lower in July, perhaps due to a shift in the fire front, change in vent structure, or another unidentified factor. Volatile organics in the vent gasses contain dangerous levels of toxic, carcinogenic, and other hazardous compounds. Benzene ranges to nearly 400 parts per billion (volume) at one vent. Toluene exceeds 104 parts per billion (volume) at the same vent.Flux rates for CO2 and CO range to 85,000 mg/s/m2 and 89 mg/s/m2, respectively, for various vents for the two measuring times. Estimates of total CO2 emissions, possibly less than 1000 t/year, are within the range of other eastern Kentucky coal fires. 相似文献
160.
Are online markets replacing or remaking second-hand markets in cities? The restructuring of secondary markets in light of virtual outlets like eBay is not well understood. In this article, we describe secondary markets and their important historic, economic, cultural, and social roles in cities. The literature on e-Commerce suggests that virtual retailers compete with bricks-and-mortar stores and potentially displace them. We question whether the internet can substitute for second-hand stores, which have traditionally relied on a loyal and local customer base, personalized shopping experiences, and surprise encounters. Given the historically embedded nature of exchange, we focus on one large Mid-western city, drawing upon survey and interview data from Chicago retailers. Our exploration of supply, demand, and geographic practices reveals subtle and complex alterations in second-hand exchange, rather than a displacement of second-hand markets by eBay. We also find substantive integration, fluidity, and hybridization within and across market sectors. Rather than supplant the production of new goods, secondary markets are intertwined with and deepen primary markets, calling into question some of the presumed benefits of and meanings associated with second-hand exchange as well as the usefulness of categorical distinctions. [Key words: secondary markets, second-hand, resale, thrift, e-commerce, eBay.] 相似文献